The present invention relates to polycrystalline diamond compacts for cutting tools, and more particularly to very fine polycrystalline diamond compacts with a grain growth inhibitor layer and reduced abnormal grain growth.
Sintered polycrystalline diamond material is known for its good wear resistance and mechanical strength, and is often used in cutting tools and rock drilling tools. To form polycrystalline diamond (PCD), diamond particles are sintered at high pressure and high temperature (HPHT sintering) to produce an ultra-hard polycrystalline structure. A catalyst material such as cobalt or another metal may be added to the diamond particle mixture prior to sintering and/or may infiltrate the diamond particle mixture during sintering in order to promote the intergrowth of the diamond crystals during HPHT sintering. The resulting PCD structure includes a network of interconnected diamond crystals or grains bonded to each other, with the catalyst material occupying the spaces or pores between the bonded diamond crystals. The diamond particle mixture may be HPHT sintered in the presence of a substrate, to form a PCD compact bonded to the substrate.
Ultra-fine PCD, such as PCD with sintered diamond grains on the order of about 1 micron in size or less, is known for its superior mechanical properties and performance. However, ultra-fine sintered PCD is difficult to create, due to the small size of the diamond particles. The very small diamond particles have a large ratio of surface area to volume, and this large surface area to volume ratio can cause abnormal grain growth of the diamond crystals during sintering. In particular, during HPHT sintering, very fine diamond particles may interconnect and grow into very large diamond grains, growing to sizes many times greater than the size of the original diamond particles in the powder mixture. As a result, the sintered material is not uniform, as the PCD structure is interrupted by areas of large, abnormal grain growth. This disparity in grain size and the lack of uniform polycrystalline structure degrade the performance and material characteristics of the sintered PCD material. It has been difficult to achieve a uniform polycrystalline structure with a very fine diamond particle mixture, such as an average particle size of 0.5 micron or less. At this size or below, abnormal grain growth is common after HPHT sintering.
Accordingly, it is known to provide a grain growth inhibitor with the diamond particle mixture in order to limit the growth of large, abnormal diamond crystals during HPHT sintering. During HPHT sintering, the grain growth inhibitor occupies space at the boundaries between diamond particles and prevents the particles from growing together into larger grain sizes. The grain growth inhibitor may be physically blended with the diamond particles prior to sintering, or may be deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD).
However, abnormal grain growth continues to be observed in PCD with ultra-fine diamond grains, in particular along the boundary between the PCD and the substrate. Accordingly, there is still a need for an ultra-fine sintered PCD compact with reduced abnormal grain growth, and a method for fabricating the same.